The present invention relates to combinations of polypropylene and ethylene/.alpha.-olefin copolymers and their application in the manufacture of mono-oriented yarns.
A process has been known for several years for the manufacture of sacks for the packaging of commodities as varied as fertilizers, chemical products, animal feedstuffs, cereals, flour, sugar, grains and seeds. This process consists in extruding polypropylene granules through an extruder, and then cooling and slitting the film thus obtained into bands. The bands are reheated in a hot air oven and then drawn on rolls, thereby producing a flat yarn called drawn tape. The drawn tape is stabilized by passing it through a second hot air oven and the stabilized drawn tape is wound in the form of reels and finally woven into sacking cloth from these reels. The sacks thus obtained have good properties of strengh, lightness, imputrescibility and dimensional stability.
French Pat. No. 1,316,312 describes compositions, suitable for the coating of copper wires, comprising 2 to 75 weight percent polypropylene (with a density of 0.87-0.92 g/cm.sup.3) and 25 to 95 weight percent of a copolymer of ethylene and an unsaturated terminal bond hydrocarbon containing more than 3 carbon atoms. The copolymer has a density between 0.90 and 0.96 g/cm.sup.3, the content of the hydrocarbon in the copolymer is between 0.1 and 50 weight percent, and the compositions have a melt index between 0.005 and 5.
The industry that manufactures woven sacks for packaging is continually searching for new materials having improved properties, especially improved tenacity.
The present invention comprises ethylene/.alpha.-olefin copolymers which, in combination with polypropylene, make possible the manufacture of mono-oriented yarns under better conditions and with improved properties in relation to the two constituents of the combination.